Rustproofing 101 – How To Apply Car Undercoating

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If you want your car to last a long time without rusting, you’ll need to apply a rust proofing undercoat.

Applying an undercoating to your car is tough, but it’s much less expensive than paying a professional. With a few basic tools and a lot of patience, you can do a great job and make sure that your car’s metals stay intact through the elements.

In this article, we’ll walk you through how to apply a rustproofing undercoat to your car.

5 Steps To Apply Car Undercoating

Step 1 – Purchase Materials

Before you begin, you’ll need to purchase the following materials for your rustproofing project:

You may not end up needing 100% of these materials, depending on how much gunk and rust has already accumulated in your undercarriage area.

You’ll get the best rustproofing results on a totally clean and brand new car, so you’ll be spending a lot of time trying to restore your car to that state before starting the rustproofing itself.

Step 2 – Setup The Hoist

You will probably need to hoist up your car to do a good job of undercoating. You can borrow a hoist from a friend or purchase one, but make sure you know how to operate it safely for your sake.

While it isn’t strictly necessary, you may also want to pick up a small automotive technician’s rolling table so that you can easily navigate from underneath the car to outside the car area without scooching along the garage floor.

Step 3 – Clean The Area

Take a quick look at the undercarriage to see how much work you will need to do. Don your gloves and goggles to be safe.

Then, prepare warm soapy water and wash down the area with a sponge, gently removing any grime and mud you find. Get the area as clean as possible and dry it off with a towel which won’t leave any fibers behind.

Next, apply the degreaser. Remove everything that the soap and water missed. By this point, you may have recognized a few early indications of rust on the surface of the metal. This is where the sandpaper and the scraper come in.

Make sure that the sandpaper is appropriate for use on metal, and then sand away the rust that you find. It might take a lot of scrubbing with the sandpaper, but you need the area to be pristine before locking it in with the rustproofing.

Wipe off the grit from the sanding process – another wash with water may be a good plan here depending on how much dust you generated.

Step 4 – Prime The Area

Once the area is ready, you’ll need to prime it, preferably with a high zinc primer. Make sure the area is dry and free of dust one final time before priming.

Priming the area is as simple as applying the primer with a brush – thinly. It’ll take a good while for the primer to dry. Apply a layer of paint over the primer – once again, thinly – if it’s necessary to restore the aesthetics of the undercarriage.

Step 5 – Apply The Undercoating

Let the paint dry fully and prepare a new brush to apply the undercoating if you are using a tar-based undercoating instead of a spray-on undercoating. Apply the undercoating in a thick layer to all of the areas of the underbody that you want to rustproof.

Apply one full coat, then let it dry for a couple of hours or however long the instructions indicate. It isn’t necessary for the coat to be dry before you apply another coat most of the time.

You can apply up to three coats before they become extraneous. You should also check the instructions on your rustproofing to see how frequently it should be refreshed.

Depending on where you’re using it, you might want to refresh your rustproofing once per year. In extreme conditions, replacing it once per season might be more appropriate.

Figure out what the right solution is for your vehicle based on where you live, how much you use your vehicle, and the context in which you use it.

Remember, your vehicle’s rustproofing only protects the surface. If rust was occurring underneath the surface of the undercarriage, your rustproofing efforts won’t do much.

You might also get a nasty surprise later on when your seemingly-pristine undercarriage starts to fall apart. Check up on the integrity of your undercarriage’s interior as frequently as possible with the help of a rustproofing professional to make sure that your home rustproofing efforts aren’t wasted.

Brett Gordon

The engine behind editing at DigMyRide and the brains behind its build. During the day, Brett is a thirty-something dude from SoCal climbing the corporate ladder, but by night, he spends his time contributing to the online world of automotive tech & trends.